/Engine/Source/Runtime/InteractiveToolsFramework/Public/BaseBehaviors/BehaviorTargetInterfaces.h
IModifierToggleBehaviorTargetis an interface that InputBehaviors can use to notify a target about modifier toggle states (like shift key being down, etc). The meaning of the modifier ID is client-defined (generally provided to the InputBehavior in a registration step)
class IModifierToggleBehaviorTarget